Select "Other provider" from the drop-down list, even if you are using a preconfigured internet telephony provider.

Try different settings for the "DTMF transmission" or ask your internet telephony provider which setting you must select.

Click "OK" to save the settings.

Besides these settings, the FRITZ!Box has no influence on whether the tones are distorted when they are transmitted to the line that was called. For example, if the internet telephony provider sends DTMF tones over the voice channel, individual tones can be distorted by other signals. In this case, the FRITZ!Box cannot resolve this issue.